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Full text of "Text Book Of Mechanical Engineering"

Double Test Diagrams.

inch, where fraction occurred. This indicates the necessity of
stating elongations somewhat as follows:—' 28*2 per cent, in a
length of 8'V or c 25*8 per cent, in a length of 10",' meaning -282
or -258 of the original length; and the breaking stress should be
measured as maximum load -~ original area. (See f. 837).

Diagrams shewing the elastic line have also been
drawn by Mr. Thos. Gray, of America, by means of the double
apparatus shown at Fig. 348. The paper drum is rotated by
worm gear, as in Fig. 343, to give the load, and there are two
pencils H and c, both connected to the specimen by wires; but
while A is connected to c through the single lever B and gives an
ordinary diagram, D gives motion to H through the triple set of
levers E, F and G, and thus the stroke of H is very greatly
magnified. Three diagrams are shewn, where the higher curves
are drawn by c, and the lower or elastic lines by H. Of course
two extension scales are required.

Admiralty Tests.—All war material must be tested as
follows, the data serving also as a general standard :—


	Material.
	Tensile breaking stress in tons per sq. in. of original area.
	Elongation.


	W. I. Ship Plates (1st class)   .,.
	( 22   ||
 ( 18 +
	


	W.I. Ship Plates (2nd  „  )   ...
	1 17  +
	


	W.I. Section Bars   .........
	22
	


	W.I. BoilerPlates  .........
	\ 21   ||
 \ 18 4-
	


	Steel Ship Plates      .........
	26 to 30
	20 y.ms;;


	'   ,,    Castings (intricate) ......
	28 minimum
	

ri
	„         „       (Roller Paths and Pivot Plates)
	36 to 40 : yield point |    at 1 8 min.
	i34°/ota2".

•fl
	,,         ,,     (Girders, Cylinders, and * Ordinary')
	•28 minimum
	i8J7.faaf

9 O
	Steel Rivets      .......... .,
	27 maximum
	

I/
	,,    Forgings (general)  ......
	28 to 35
	28 to 2A °l in. 2'

^H  i 0
	,,        „        (Piston Rods) ,..
	32 to 35
	*.\j \.\j *i+   IOIM*,
 28 to 24 7 i& 2;/

o
	„        ,,        (Rollers and Roller Paths)
	| 38 to 45
	22 to 16 7 in. 2^

frT
	„    Plates       ............
	28 to 32
	20 */a in 8"


	Gun Metal (ordinary)      ......
	14 minimum
	


	,,        (for hydraulics)
	f»
	3} f°0 in 2f>


	^ Manganese Bronze   .........
	28
	25 9/l in 4"